Semiconductor light emitting device

ABSTRACT

A high external quantum efficiency is stably secured in a semiconductor light emitting device. At least one recess and/or protruding portion is created on the surface portion of a substrate for scattering or diffracting light generated in a light emitting region. The recess and/or protruding portion has a shape that prevents crystal defects from occurring in semiconductor layers.

FIELD OF THE INVENTION

[0001] The present invention relates to a semiconductor light emittingdevice, in particular, to a nitride-based compound semiconductor lightemitting device wherein a recess or a protruding portion is provided ina substrate so that defects do not occur in the semiconductor andthereby, the direction of guided light is changed in a semiconductorlayer to increase the external quantum efficiency.

DESCRIPTION OF THE PRIOR ART

[0002] In a semiconductor light emitting device, for example, in a lightemitting diode (LED), an n-type semiconductor layer, a light emittingregion and a p-type semiconductor layer are essentially made to grow ontop of a substrate to form a layered structure while a structure isadopted wherein electrodes are formed on the p-type semiconductor layerand on the n-type semiconductor layer. Light, generated throughrecombination of holes and electrons that have been injected through thesemiconductor layers to the light emitting region, is emitted through alight transmitting electrode on the p-type semiconductor layer or fromthe substrate. Here, the light transmitting electrode means an electrodethat allows light to be transmitted through the electrode and that ismade of a metal thin film or of a transparent conductive film formed onalmost the entirety of the p-type semiconductor layer.

[0003] In order to control the layered structure of a light emittingdiode at atomic level, the substrate is processed so that the flatnessthereof becomes of a level of a mirror surface. Semiconductor layers, alight emitting region and electrodes on top of a substrate form alayered structure wherein the layers are parallel to each other. Sincethe index of refraction of the semiconductor layers is high, a lightguide is formed between the surface of the p-type semiconductor layerand the surface of the substrate. That is to say, the light wave guideis made in a structure wherein the semiconductor layers having a highindex of refraction are sandwiched between the substrate and the lighttransmitting electrode having a low index of refraction.

[0004] Accordingly, in the case that light enters the inner-surface ofthe electrode or the outer-surface of the substrate at an angle largerthan a critical angle, the light is layers trapped within the lightguide. The light is reflected at the interface between the electrode andthe p-type semiconductor layer and at the surface of the substrate topropagate laterally in the layered structure of the semiconductor. Sincethe light loses its energy during the propagation in the semiconductorlayer, the external quantum efficiency of the device is lowered. That isto say, the light that has entered the interface at an angle larger thanthe critical angle repeat reflection in the light guide and finally beabsorbed. Therefore, the emitted light is attenuated and cannot beeffectively emitted to the outside, which lowers the external quantumefficiency of the device.

[0005] A method has been proposed wherein a light emitting diode chip isprocessed to be of a hemispherical form or of a truncated pyramidal formso that light generated in the light emitting region is made to enterthe surface at an angle smaller than the critical angle. However, it isdifficult to make such a chip.

[0006] Also, a method has also been proposed wherein the top surface orthe side of a light emitting diode is roughened. However, with such amethod, there is a risk that the p-n junction may be partially damagedand the effective light emitting region is reduced.

[0007] Another method has been proposed wherein light generated in thelight emitting region is scattered by creating a recess or protrusion inthe surface of a substrate so that the external quantum efficiency isincreased (see Japanese laid-open patent No. 11-274568 (1999)).According to this method, in a GaN-based LED wherein the sapphiresubstrate, n-type GaN, p-type GaN and a transparent electrode aresequentially layered, the surface of the sapphire substrate is randomlyroughed by means of a mechanical polishing or etching. Thereby, lightthat has entered the sapphire substrate is scattered so that theexternal quantum efficiency is increased.

SUMMARY OF THE INVENTION

[0008] However, in the above-described conventional light emittingdiode, the external quantum efficiency may be lowered by the recess orthe protrusion. That is to say, in the case that the surface isroughened at random to generate recess or protrusion, the crystallinityof the grown GaN may be lowered. Therefore, the luminous efficiency,i.e. internal quantum efficiency, in the GaN semiconductor layers islowered, and thus the external quantum efficiency is lowered rather thanraised. In addition, if the light absorption within the light guide isso large, the external quantum efficiency does not reach a sufficientlevel only with the randomly roughed surface.

[0009] Therefore, an object of the present invention is to provide asemiconductor light emitting device wherein an improved external quantumefficiency can be stably secured.

[0010] According to the present invention, a semiconductor lightemitting device has a light emitting layer and two semiconductor layerswhich are formed on the surface of the substrate made of differentmaterial from that of the semiconductor layers. The light emittingregion emits light to outside through the semiconductor layer orsubstrate. The LED is characterized in that at least one recess and/orprotrusion is formed on the surface of the substrate so that the lightgenerated in the light-emitting region is scattered or diffracted, andthat the recess and/or protrusion prevents crystal defects fromoccurring in the semiconductor layers. Here, “prevent crystal defectfrom occurring” means that the recess or protrusion causes neither anmorphological problem, such as “pits”, nor increase of dislocations inthe semiconductor layers.

[0011] One of the characteristics of the present invention is in thatthe recesses and/or protrusions, having such shapes as to preventdefects from growing in a semiconductor layer on the substrate, areformed on the surface of the substrate. The recesses and/or protrusionsare formed not at the interface between the semiconductor layer and theelectrode, but at the interface between the semiconductor layer and thesubstrate. This improves the crystallinity of the light emitting region(active layer) and increase the output power of the device. Inparticular, in the case of a gallium nitride-based componentsemiconductor light emitting device, a substrate, an n-side nitridesemiconductor layer, a light emitting region (active layer) and a p-sidenitride semiconductor layer are layered, in this order, wherein the filmthickness of the p-side nitride semiconductor layer is less than that ofthe n-side nitride semiconductor layer. Therefore, recesses orprotruding portions are provided at the interface between thesemiconductor layer and the substrate rather than at the interfacebetween the semiconductor layer and the electrode and thereby, theeffect due to unevenness is mitigated by the thick n-side nitridesemiconductor layer so that the crystallinity of the light emittingregion (active layer) can be maintained in an good condition.

[0012] In the case of a semiconductor light emitting device having aconventional flat substrate, light propagated through the semiconductorlayer in the lateral direction attenuates before emerging from thesemiconductor layer because a portion thereof is absorbed by thesemiconductor layer or by the electrode during propagation. On thecontrary, according to the present invention, light propagated in thelateral direction in the case of a conventional flat substrate isscattered or diffracted by recesses and/or protruding portions andfinally efficiency emitted from the upper semiconductor layer or thelower substrate. As a result, the external quantum efficiency can begreatly increased. That is to say, first, light flux directed upward ordownward from the substrate increases through the scattering anddiffracting effects of light due to the unevenness so that the frontalbrightness, which is the brightness of the light observed from the frontof the light emitting surface of the device, can be enhanced. Second,light propagated in the lateral direction is reduced through thescattering and diffracting effects of the unevenness so that the totalamount of light emission can be enhanced by reducing the absorption lossduring propagation.

[0013] In addition, crystal defects do not increase in the semiconductorlayer even in the case that recesses and/or protruding portions arecreated in the surface portion of the substrate. Therefore, theabove-described high external quantum efficiency can be stably secured.In the present invention, it is preferable for the inside of therecesses or the surroundings of the protruding portions to be completelyfilled in with a semiconductor layer. This is because, in the case thata cavity exists inside a recess or in the surroundings of a protrudingportion, the scattering or diffracting effects are prevented. Thislowers the efficiency of the light emission.

[0014] Either recesses or protruding portions may be created in thesurface portion of the substrate. Combination of recesses and protrudingportions may be created. Such combination may provide similar workingeffects. However, protrusions are more preferable than recesses, becauseit is easier to completely fill the surrounding of protrusions ratherthan recesses. If a cavity is remained around the protrusions orrecesses, the scattering or diffracting effects are prevented, whichlowers the output power of the device.

[0015] Shapes of recesses and/or protruding portions for preventing thegrowth of defects in the semiconductor layer are, concretely, shapeshaving, as component sides, lines that cross a plane approximatelyparallel to the stably growing face of the semiconductor. In otherwords, if the shapes are observed from the upper side of the substrate,the shapes have lines which are unparallel to the stably growing face ofthe semiconductor. Here, the stably growing face indicates the surfaceon which the growth rate of the material made to grow is slower than anyother surface. Generally, the stably growing surface is observed as afacet during the crystal is grown. For example, in the case of galliumnitride semiconductors, the stable growing faces are the ones parallelto the A axis (especially, M face). Therefore, the recesses orprotruding portions are formed, when observed from the upper side, inpolygon of which component lines are unparallel to the A axis-parallelplane. In other words, in polygon of which component lines areunparallel to A axis. In the case that the recesses and/or protrudingportions have, as component sides, lines approximately parallel to thestably growing face of the semiconductor, crystal defects occur in suchportions at the time of the film growth of the semiconductor layer andthese defects lower the internal quantum efficiency which causes thelowering of the external quantum efficiency.

[0016] More concretely, the recesses and/or protruding portions can be,for example, polygons, triangles, parallelograms or hexagons, and arepreferably equilateral triangles, rhomboids or regular hexagons having avertex in a plane approximately parallel to the stably growing face ofthe semiconductor and having, as component sides, lines that cross theplane approximately parallel to the stably growing face of thesemiconductor.

[0017] Here, in the present specification, the phrase “a recess or aprotruding portion is in the form of a polygon” means that the shape ofthe recess or of the protruding portion in the plan view observed fromabove is in the form of a polygon. It is not necessary to form acomplete polygon. The edge of the polygons may be rounded as a result ofprocessing.

[0018] For example, in the case that a GaN-based semiconductor is madeto grow on a C plane of a sapphire substrate, the growth starts inhexagonal islands having planes parallel to A axis, which planes are thestably growing face of a GaN-based semiconductor, as a component side,and then, these islands are connected to become a uniform semiconductorlayer. Therefore, a regular hexagon having an A axis as a componentside, is assumed and a recess or a protruding portion is created in apolygon (for example, a triangle, a hexagon, or the like) having, as acomponent side, a line perpendicular to a segment that connects thecenter of the above hexagon and the vertex. A GaN-based semiconductorthat is flat and has an excellent crystallinity can be made to grow ontop of a sapphire substrate wherein unevenness is created in the abovemanner.

[0019] In addition, though one recess and/or protruding portion may besufficient for the invention, when a pattern is formed by repeating theshape of a recess or of a protruding portion, the efficiency ofscattering or diffraction of light increases so that the externalquantum efficiency can be further increased. Here, in the presentinvention, even in the case that recesses and/or protruding portions areprovided on a substrate in a repeating pattern, the semiconductor layeris made to grow so that local crystal defects due to recesses or toprotruding portions can be prevented and thereby, the entire surface ofthe substrate can be used as a light emitting surface.

[0020] The present invention is characterized in that recesses and/orprotruding portions are created in the surface portion of a substrate toscatter or diffract light. The material itself for the substrate and forthe semiconductor of the light emitting device is not directly relatedto the invention and any material, for example, III-V groupelements-based semiconductors, concretely, a GaN-based semiconductor,can be utilized for a semiconductor layer of a semiconductor lightemitting device. The stably growing face of a GaN-based semiconductorlayer is an M plane {1-100} of a hexagonal crystal. Here, {1-100}represents all of (1-100), (01-10) and (-1010). An M face is one of thefaces parallel to A axis. In some growing conditions, the stably growingfaces of GaN-based semiconductors are the faces parallel to A axis otherthan M faces.

[0021] As for the substrate, a sapphire substrate, an SiC substrate or aspinel substrate can be used. For example, a sapphire substrate having aC plane (0001) as a main surface can be used as the above-describedsubstrate. In this case, an M plane, which is the stably growing face ofa GaN-based semiconductor layer, is a plane parallel to an A plane{11-20} of a sapphire substrate. Here, {11-20} represents all of(11-20), (1-210) and (-2110).

[0022] The depths of recesses or the steps of protruding portions are 50Å or more, and it is important for them to be equal to or less than thedimension of the thickness of the semiconductor layer made to grow onthe substrate. The depths or the steps must be at least λ/4 or more whenthe wavelength of the emitted light (for example, 206 nm to 632 nm inthe case of an AlGaInN-based light emitting layer) is λ in order tosufficiently scatter or diffract light. However, the depths of therecesses or the steps of protruding portions becomes larger than thethickness of the semiconductor layer, which is made to grow on thesubstrate, it becomes difficult for a current to flow in the lateraldirection within the layered structure so that the efficiency of thelight emission is lowered. The surface of the semiconductor layer mayhave recesses and/or protruding portions. Though it is preferable forthe depths or the steps to be of λ/4 or more in order to sufficientlyscatter or diffract light, depths or steps of λ/4n (n is the index ofthe refraction of the semiconductor layer) or more can gain the effectsof scattering or diffraction.

[0023] It is important for the size of the recesses and/or protrudingportions (that is to say, the length of one side that becomes acomponent side of a recess and/or protruding portion) and for theintervals between the recesses and/or protruding portions to be at leastthe size of λ/4 or more when the wavelength in the semiconductor is λ(380 nm-460 nm). This is because, unless the size is at least λ/4 ormore, light cannot be sufficiently scattered or diffracted. Though it ispreferable for the size of, and the intervals between, the recessesand/or protruding portions to be of λ/4 or more in order to sufficientlyscatter or diffract light, size or intervals of λ/4n (n is the index ofthe refraction of the semiconductor layer) or greater, can gain theeffects of scattering or diffraction. The size of, and the intervalsbetween, the recesses and/or protruding portions may be 100 μm or lessfrom the point of view of manufacturing. Furthermore, it is preferablefor the size of, and the intervals between, the recesses and/orprotruding portions to be recesses 20 μm or less in order to increasethe scattering surfaces.

[0024] Since the total film thickness of the semiconductor layers is, ingeneral, 30 μm or less, it is preferable for the pitch of the unevennessto be 50 μm or less from the point of view of effective reduction in thenumber of total reflection due to scattering or diffraction.Furthermore, it is preferable for the pitch of the unevenness to be 20μm or less from the point of view of the crystallinity of GaN layer.More preferably, the pitch of the unevenness are less than 10 μm. Thisincreases a scattering efficiency and an out-put power of a device.Here, the pitch of the unevenness indicates the minimum distance fromamong the distances between the centers of the neighboring recesses orof the neighboring protruding portions.

[0025] Next, as for the shape of the unevenness in the cross section, itis preferable for a protruding portion to be a trapezoid and for arecess to be a reverse trapezoid, as shown in FIG. 9. Such a shape inthe cross section enhances the efficiency of scattering and diffractionof light. It is not necessary to make the shape in the cross sectioncompletely trapezoidal or reverse trapezoidal. The edge of the trapezoidmay be rounded during forming the unevenness. Here, a taper angle θindicates, in the case of protrusions, the angle between the top andside surface, and, in the case of recesses, the angle between the bottomand side surface, as shown in FIG. 9. For example, if the angle θ is 90degrees, the protrusions or recesses has a square cross section. If theangle θ is 180 degrees, the protrusions or recesses are flattened. Inorder to fill the unevenness by the semiconductor, the taper angle θshould be larger than 90 degrees. From the view point of increasing theoutput power by the scattering or diffraction, the taper angle θ ispreferably more than 90 degrees, more preferably more than 105 degrees,much more preferably more than 115 degrees. On the other hand, too largetaper angle decreases a scattering efficiency and induces pits insemiconductor layers. The taper angle is preferably not more than 160degrees, more preferably not more than 150 degrees, much more preferablynot more than 140 degrees.

[0026] Here, in the case that the sides of recesses and/or protrudingportions are inclined, the sides and the intervals of the unevenness isdefined by the length in the top surface of the substrate (upper surfaceof protruding portions in the case of protruding portions and flatsurface of the substrate in the case of recesses).

[0027] In the present invention, it is preferable to form a metal layerwith openings as an ohmic electrode. In the case an electrode entirelycovering the surface of the semiconductor layer and having openings isformed on semiconductor layers, the electrode could cooperate with theunevenness on the substrate to remarkably increases the utilizationefficiency of the light. Especially, it is preferable that each openingsinclude at least one step portion of the unevenness on the substrate.The reason of this is assumed as follows: First, when the light emittingdevice having the unevenness on its substrate is observed from thefront, step portions of the protrusions and/or recesses seems brighterthan flat portions of the substrate. Accordingly, if openings are formedabove the step portions of the protrusions and/or recesses, the outputpower of the device is remarkably improved. Second, in a device havingthe unevenness on the substrate, light that inherently propagateslaterally or downwardly is scattered or diffracted to go upwardly.However, if a conventional transparent electrode is formed to cover theentire surface of the device, the scattered or diffracted light ispartly absorbed and weakened by the electrode. Accordingly, on asemiconductor layer on a substrate with the unevenness, an electrode,which may be either transparent or opaque, with openings are preferablyformed to expose a part of the semiconductor layer. This helps thescattered or diffracted light to go out of the device and improves theefficiency of the light utilization.

[0028] In the case of the gallium nitride semiconductor, including asemiconductor having at least gallium and nitrogen, a portion near theperipheral of the p-side electrode, which is formed on the p-typesemiconductor layer, lights brighter than other portions. By formingopenings in the electrode, not only the light absorption is decreased,but also the length of the peripheral of the p-side electrode, where thelight strongly emits, is increased. Therefore, the efficiency of thelight utilization is improved. It is preferable for L/S≧0.024 μm/μm² tobe fufilled wherein the total area of the ohmic electrode including theopenings is S and the total sum of the length of the inner periphery ofthe openings is L. This improves the efficiency of the lightutilization, by increasing the length of the peripheral of theelectrode.

[0029] As for a material favorable for the ohmic electrode withopenings, an alloy or a multilayer film including at least one typeselected from the group consisting of Ni, Pd, Co, Fe, Ti, Cu, Rh, Au,Ru, W, Zr, Mo, Ta, Pt, Ag and oxides of these as well as nitrides ofthese can be cited. Especially an alloy or a multiplayer film includingone type selected from Rhodium(Rh), Iridium(Ir), Silver(Ag) andAluminum(Al) is preferable.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030]FIG. 1 is a cross sectional view showing a semiconductor lightemitting device according to a preferred embodiment of the presentinvention;

[0031]FIG. 2 is a view showing an example of a pattern of a recessaccording to the above-described embodiment;

[0032]FIG. 3 is a schematic view showing relationships between a stablygrowing face of a nitride semiconductor and a shape of a recess;

[0033]FIG. 4 represents views showing manufacturing steps of the firstembodiment;

[0034]FIG. 5 represents SEM photographs for observing processes of thegrowth of gallium nitride on a sapphire substrate wherein protrudingportions are created;

[0035]FIG. 6 represents diagrams showing processes of the growth ofgallium nitride on a sapphire substrate wherein a protruding portion iscreated;

[0036]FIG. 7 represents diagrams schematically showing manners ofpropagation of light according to the present invention in comparisonwith those in conventional structures;

[0037]FIG. 8 represents cross sectional views additionally showing otherembodiments;

[0038]FIG. 9 is a cross-sectional view of the recess and/or protrudingportions.

[0039]FIG. 10 is a graph showing the relationships between the angle ofinclination of a side of a recess and the output of emitted light;

[0040]FIG. 11 represents examples of other patterns of a recess or of aprotruding portion;

[0041]FIG. 12 represents diagrams for describing other embodimentswherein a recess or a protruding portion is a regular hexagon;

[0042]FIG. 13 is graph showing the relationships between L/S (ratio ofinner circumference L of an opening to area S of p-side ohmic electrode)and the output of emitted light;

[0043]FIG. 14 represents diagrams showing various variations of the modeof p-side ohmic electrode;

[0044]FIG. 15 represents schematic diagrams showing the relationshipsbetween the forms of cross sections of edge portions of the p-side ohmicelectrodes and light emissions;

[0045]FIG. 16 is a view of a semiconductor light emitting device, viewedfrom above, according to another embodiment of the present invention;and

[0046]FIG. 17 is a view of a semiconductor light emitting device, viewedfrom above, according to still another embodiment of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0047] In the following the present invention is described in detailbased on the concrete examples shown in the drawings. FIGS. 1 and 2 showa semiconductor light emitting device according to a preferredembodiment of the present invention. In these figures a C plane (0001)sapphire substrate having an orientation flat in the A plane (11-20) isused as a substrate 10 while recesses 20 are created in a repeatedpattern in the surface portion of this sapphire substrate 10. In FIG. 2the substrate is etched so that the hatched portion remains.

[0048] This recess 20 forms an equilateral triangle having a vertex in aplane parallel to the stably growing face (1-100), (01-10), (-1010) ofthe GaN-based semiconductor 11, which grows on the sapphire substrate10, that is to say, the M plane and having, as a component side, a linethat crosses a plane approximately parallel to the above-describedstably growing face. That is to say, from a top view of the substrate,an equilateral triangle that forms a recess 20 has a vertex at aposition wherein the M plane cross each other and each component side ofthe equilateral triangle crosses the M plane at an angle of 30 degreesor 90 degrees. More concretely, as shown in FIG. 3, each component sideof a recess 20 is perpendicular to a line segment connecting the centerof a regular hexagon having the M plane of GaN semiconductor 11 as acomponent side and the vertex when recess 20 is viewed from above. Whenobserved from directly above the substrate, M faces of the GaN basedsemiconductor are parallel to A axis.

[0049] In addition, the depth of recess 20 is approximately 1 μm and, asfor the size thereof, one side “a” is 10 μm while, as for the intervalsbetween recess 20 and recess 20, one side corresponds to an interval is10 μm.

[0050] An n-type GaN-based semiconductor layer 11, an MQW light emittingregion 12 on n-type GaN-based semiconductor layer 11 and furthermore, ap-type AlGaN/p-type GaN-based semiconductor 13 on MQW light emittingregion 12 are formed on top of the above-described sapphire substrate10.

[0051] In the case that a semiconductor light emitting device accordingto this example is manufactured, an SiO₂ film 30 that becomes an etchingmask is formed sapphire substrate 10, as shown in FIG. 4A.

[0052] Next, a photomask in the shape of an equilateral triangle havinga side of 10 μm is utilized and the photomask is adjusted so that oneside of the equilateral triangle becomes perpendicular to theorientation flat, wherein each side of the equilateral triangle becomesapproximately parallel to the plane (1-100), (01-10), (-1010), that isto say, the M plane, of the sapphire so that SiO₂ film 30 and sapphiresubstrate 10 are etched by approximately 1 μm by means of RIE, as shownin FIGS. 4B and 4C, and after that, SiO₂ film 30 is removed, as shown inFIG. 4D, so that a repeated pattern of recesses 20, as shown in FIG. 2,is formed in the surface portion of sapphire substrate 10.

[0053] An n-type GaN semiconductor layer 11, an MQW light emittingregion 12 on-type GaN semiconductor layer 11 and a p-type AlGaN/p-typeGaN semiconductor layer 13 on MQW light emitting region 12 are made togrow on top of sapphire substrate 10 having the repeated pattern ofrecesses 20.

[0054] Since the lattice of GaN grows with a shift of 30 degrees from alattice of sapphire substrate 10, the repeated pattern of recesses 20formed on sapphire substrate 10 forms a polygon having sidesapproximately parallel to the A plane of GaN (11-20), (1-210), (-2110),having a vertex in the stably growing face of GaN (1-100), (01-10),(-1010) and not having a line parallel to the stably growing face of GaN(1-100), (01-10), (-1010), that is to say, the M plane.

[0055] These arrangements improves the crystallinity of GaN. Themechanism of improving crystallinity will now be discussed with anexample of protruding portions, since the mechanism is the same as inthe case of recesses. FIGS. 5A and 5B are SEM photographs of GaN duringthe process of growth on top of sapphire substrate 10 wherein protrudingportions 20 in an equilateral triangle shape are created wherein FIG. 5Ashows a view as observed from above while FIG. 5B shows a diagonal viewfrom above. As shown in FIGS. 5A and 5B, when GaN is made to grow on thesapphire substrate 10, the growth of GaN progresses from the top surfaceof protruding portions 20 and from the flat surface wherein protrudingportions 20 are not created so that the side surfaces and the vicinitythereof of protruding portions 20 are finally filled in with GaN.Accordingly, in the case that the stably growing face of GaN and thesides of protruding portions 20 are parallel to each other, it becomesdifficult for the sides and vicinity of protruding portions 20 to becomefilled in with GaN so that the crystallinity of GaN is lowered.

[0056] Therefore, it is preferable to form component sides of protrudingportions 20 to cross (not to become parallel to) the M plane, which isthe stably growing face of GaN. Furthermore, it is preferable, as shownin FIGS. 5A and 5B, for the component sides of protruding portions 20 tobe formed so as to be perpendicular to the line segment connecting thecenter of a hexagon having the M plane, which is the stably growing faceof GaN, as component sides and the vertex. By creating protrudingportions 20 in such a manner, GaN having an excellent crystallinity thatfills in the inside of protruding portions 20 to provide flatness can begained.

[0057] It is assumed that this is because the growth rate of GaN becomeshigher in a portion wherein GaN that has grown from the top surfaces ofprotruding portions 20 and GaN that has grown from the flat surfacewherein protruding portions 20 are not created make a junction. As shownin FIG. 5B, GaN has grown from the top surfaces of protruding portions20 in the shape of a hexagon having the M plane as component sides. Thegrowth rate of GaN becomes higher in the vicinity of the side planes ofprotrusions, where GaN that has grown from the top surfaces ofprotrusions 20 and GaN that has grown from the flat surface makecontact. Accordingly the growth of GaN in the vicinity of the sides ofprotruding portions catches up with that in the other regions andthereby, flat GaN is gained.

[0058] This is schematically described using FIGS. 6A to 6F. When, asshown in FIG. 6A, protruding portions 20 are created in sapphiresubstrate 10 and GaN is made to grow on top of that, GaN grows, as shownin FIGS. 6B and 6C, from the top surfaces of protruding portions 20 andfrom the flat surface in which protruding portions 20 are not created,while growth slows in the vicinity of the sides of protruding portions20. As shown in FIGS. 6D and 6E, however, when GaN 11 a, which has grownfrom the top surfaces of protruding portions 20, and GaN 11 b, which hasgrown from the flat surface, meet, the growth rate of GaN becomes higherthere. Therefore, the growth significantly progresses in the vicinity ofsides of protruding portions 20, wherein growth had been behind. Then,as shown in FIG. 6F, GaN 11 having flatness and an excellentcrystallinity grows. On the contrary, in the case that the surface onwhich GaN stable grows and the sides of protruding portions 20 areparallel to each other, the growth rate does not increase in thevicinity of the sides of the protruding portions 20 and therefore, itbecomes difficult to fill in the vicinity of the sides of recesses 20 sothat the crystallinity of the GaN is lowered.

[0059] After that, a device process is carried out and electrodes andthe like are appropriately formed so that LED chips completed.

[0060] When holes and electrons are injected from n-type GaNsemiconductor layer and p-type AlGaN/p-type GaN semiconductor layer 13to MQW light emitting region 12 so that recombination is carried out,light is generated. This light is emitted from sapphire substrate 10 orp-type AlGaN/p-type GaN semiconductor layer 13.

[0061] In the case of a semiconductor light emitting device having aconventional flat substrate, as shown in FIG. 7A, when light from lightemitting region 12 enters the interface between p-type semiconductorlayer 13 and the electrode or the surface of substrate 10 at an anglelarger than the critical angle, light is trapped within the light guideso as to propagate in the lateral direction.

[0062] On the contrary, in a semiconductor light emitting device of thepresent example, light entering the interface between p-typesemiconductor layer 13 and the electrode or the surface of substrate 10at an angle larger than the critical angle is scattered or diffracted byrecess 21, as shown in FIG. 7B, to enter the interface between p-typesemiconductor layer 13 and the electrode or the surface of substrate 10at an angle less than the critical angle to be emitted.

[0063] In the case that the contact electrode on p-type semiconductorlayer 13 is a light transmitting electrode, the present example iseffective for an FU (face up) semiconductor light emitting device and,in the case that the contact electrode is a reflecting electrode, thepresent example is effective for an FD (face down) semiconductor lightemitting device. However, if a reflecting electrode has apertures, thepresent example may be used with an FU type. This embodiment isespecially effective.

[0064]FIG. 8 shows a semiconductor light emitting device according toanother embodiment of the present invention. The device is formed sothat the sides of the steps of recesses 20 are inclined in theembodiment shown in FIG. 8A. In addition, protruding portions 21, inplace of recesses 20, are formed on the surface portion of substrate 10in the embodiment shown in FIG. 8B and, in this example, protrudingportions 21, of which the cross sections are of a semi-circular shape,are formed. Furthermore, an n-type semiconductor layer 11, a lightemitting region 12 and a p-type semiconductor layer 13 form planes withrecesses in accordance with recesses 20 in the embodiment shown in FIG.8C.

[0065]FIGS. 7C and 7D show examples of light propagation in theembodiments shown in FIGS. 8A and 8C. It can be seen that light isefficiently emitted in both cases. In particular, surfaces (sides ofrecesses or of protruding portions) connected to the surfaces ofprotruding portions and to the surfaces of recesses having lines (alsoreferred to as the component sides of a polygon), which cross a planeapproximately parallel to the stably growing face of the semiconductorlayers as interfaces, are formed so as to be inclined relative to thedirection in which the semiconductor is layered, as shown in FIG. 8A andthereby, the effects of light scattering or light diffraction notablyincrease so that the efficiency of light emission significantlyincreases. It is considered that one factor contributing to this is anincrease in the number of occurrences of light scattering or lightdiffraction due to increase in the area of the surfaces (sides ofrecesses or of protruding portions) connected to the surfaces ofrecesses and to the surfaces of protruding portions as a result of theprovision of the inclination.

[0066] In other words, it is preferable for the shape of the unevennessin the cross section to be a trapezoid in the case of a protrudingportion and to be a reversed trapezoid in the case of a recess, as shownin FIG. 9. By providing such a shape in the cross section, theprobability of occurrence of scattering and diffraction of propagatedlight is increased so that the absorption loss of light at the time ofpropagation can be reduced. Here, the taper angle of the sides ofrecesses and/or protrusions indicates, as shown in FIG. 9, the angleformed between the top surface and a side in the case of a protrudingportion and angle formed between the bottom surface and a side in thecase of a recess. For example, if the taper angle is 90 degrees, thecross section of the protrusions and/or recesses will be a square, andif the angle is 180 degrees, the protrusions and/or recesses will becomeflat.

[0067] In order to fill the unevenness by semiconductor layers, thetaper angle of the protrusions and/or recesses must not be less than 90degrees. From the view point of improving an output power by anunevenness, the taper angle of the sides of recesses and/or protrudingportions is preferably more than 90 degrees, more preferably more than105 degrees, much more preferably more than 115 degrees. On the otherhand, too large taper angle decreases a scattering efficiency andinduces pits in semiconductor layers. The taper angle is preferably notmore than 160 degrees, more preferably not more than 150 degrees, muchmore preferably not more than 140 degrees.

[0068]FIG. 10 is a graph showing the relationships between the angle ofinclination of the sides of recesses and the LED power. Here, a similartendency as in the graph can be gained when the angle of inclination isregarded as that of the sides of the protruding portions. Thelongitudinal axis of the graph of FIG. 10 indicates the ratio of outputin the case that the LED output when a flat substrate (=taper angle is180 degrees) is used is set as 1 while the lateral axis of the graphindicates the angle of inclination of the sides of recesses. As shown inthe graph, the output of the LED changes significantly when the angle ofinclination (angle formed between the bottom surface of a recess and aside) is changed between 90 degrees and 180 degrees.

[0069]FIG. 11 shows examples of other shapes of recesses 20 orprotruding portions 21. In the figure, the hatched portions are theportions that are not etched.

[0070] In addition, in the case that recesses 20 or protruding portions21 are regular hexagons, the regular hexagons are placed in thedirection shown in FIG. 12B, not in the direction shown in FIG. 12C,relative to orientation flat surface A of sapphire substrate l shown inFIG. 12A. As described above, in the case that GaN is made to grow onthe C face of the sapphire substrate, the A face of the sapphiresubstrate and the M face of GaN become parallel to each other, whenobserved from above the substrate. Accordingly, the regular hexagonshaving uneven surfaces are arranged as shown in FIG. 12B and thereby,each of the component sides of the regular hexagons becomesperpendicular to any of surface M, which is the stably growing face ofGaN. In other word, the hexagonal protrusions and/or recesses have thecomponent sides that are perpendicular to a segment that connects thecenter and vertex of the hexagon having the M face of GaN as itscomponent side.

[0071] In addition, according to the present invention, a conventionalsemiconductor layer, such as a nitride semiconductor layer, is formed ona substrate in which unevenness is provided so that defects do not occurin the semiconductor and additionally, electrodes and the like areformed in a device, wherein, though other parts of the configuration arenot specifically limited, remarkable effects are additionally gained bymaking the other parts of the configuration be as follows.

[0072] (1) Form and Material of Electrode

[0073] <1> Open Electrode

[0074] It is necessary to provide an electrode on top of thesemiconductor layer on the surface of a semiconductor light emittingdevice and generally, a transparent electrode is formed on the entiretyof the surface of the semiconductor layer when the semiconductor layeris a semiconductor layer having a comparatively high specific resistancewherein current dispersion hardly occurs, such as in a p-type nitridesemiconductor layer. However, at the time when light propagates withinthe light guide formed in the structure of a light emittingelectrode-semiconductor layer-substrate, emitted light is absorbed orattenuated by not only the semiconductor layer but, also, by the lighttransmitting electrode and by the substrate as a result of the effectsof “leakage” of reflected light. In particular, a transparet electrodesignificantly affects the attenuation of emitted light because thegeneral component materials thereof (Au/Ni, for example) has a highratio of light absorption in the short wavelength range.

[0075] Therefore, it is preferable to form, as an electrode, a metalfilm having an opening in a light emitting device according to thepresent invention. Especially, it is preferable that each opening has inits inside at least one step portion of the unevenness of the substrate.By forming an electrode with openings on the semiconductor layers, theopenings let the light go through so that the absorption by theelectrode is reduced. It is preferable that a plurality of openings isformed in the metal layer. From the view point of improving anefficiency of light utilization, it is also preferable to make the areaof the openings as large as possible. On the electrode with openings, apad electrode for connecting the device with an outer circuit ispreferably formed.

[0076] In addition, in the case of a nitride semiconductor lightemitting device, in particular, in the case of a gallium nitride-based(at least gallium and nitrogen are included) semiconductor lightemitting device, an electrode having light transmission, preferablythrough the entirety of the surface, is, in many cases, provided as a pelectrode on the p-type nitride semiconductor layer and then, the deviceexhibits the property wherein the light absorption in the light emittingelectrode becomes great so that the periphery and the vicinity of theperiphery of the p electrode provided on the p-type nitridesemiconductor layer emits light that is more intense than that emittedfrom other parts of the device. Therefore, openings may be provided inthe light transmitting electrode. Thereby, light absorption is reducedand the peripheral portion that emits intense light is increased in areaso that the efficiency of light emission is increased. In this case, itis preferable for the area of the openings to be provided as large aspossible from the point of view of increase in the efficiency of thelight emission and by making the length of the peripheral portion of thep electrode as long as possible, the efficiency of the light emission isfurther increased.

[0077] It is preferable for the electrode formed on the surface of thesemiconductor layer to be an electrode having an opening, as describedabove, because the effect of recesses and/or protruding portions on thesurface of substrate is much higher with an electrode having an opening.There may exist two reasons. First, when observed from the front of thedevice, the brightness of edges of recesses and/or protruding portionsis higher than other portions. Therefore, by forming the openings abovethe edges of the recesses and/or protrusions, the output power isconsiderably increased. Second, light that has reached to upper areasthrough scattering or diffraction has a low intensity. Therefore, mostof the light that has reached to upper areas through scattering ordiffraction is absorbed by the light transmitting electrode in theconfiguration wherein a conventional light transmitting electrode isprovided on the entirety of the surface. In the case that asemiconductor layer is formed on a substrate wherein unevenness isprovided, openings are provided in the light transmitting electrode or anon-light transmitting electrode so that the semiconductor layer ispartially exposed and thereby, light having a low intensity is easilyemitted to the outside so as to significantly increase the efficiency oflight emission.

[0078] <2> Material for Open Electrode

[0079] As described above, in the case of a nitride semiconductor lightemitting device, in particular, in the case of a gallium nitride-based(at least gallium and nitrogen are included) semiconductor lightemitting device, an electrode having light transmission almost theentirety of the surface of a p-type nitride semiconductor layer isprovided as a p electrode and in a more favorable embodiment, anelectrode provided with openings is formed on almost the entirety of thep-type nitride semiconductor layer so that the efficiency of the lightemission is increased. At this time, a metal or an alloy made of twotypes of metal is used as a material used in the electrode and a singlelayer or a plurality of layers can be formed. A metal material of a highreflectance for at least the wavelength of the emitted light ispreferably used as the material for this electrode. This reduces thecomponents of light absorbed by the electrode so that the efficiency ofthe light emission to the outside can be increased.

[0080] As for a material favorable for the open electrode, an alloy or amultilayer film including at least one type selected from the groupconsisting of Ni, Pd, Co, Fe, Ti, Cu, Rh, Au, Ru, W, Zr, Mo, Ta, Pt, Agand oxides of these as well as nitrides of these can be cited. Anexternal ohmic contact can be gained between the above and a p-typesemiconductor layer by annealing the above at a temperature of 400° C.,or higher. In particular, a multilayer film wherein Au is layered on Niis preferable. As for the total film thickness of the open electrode, 50Å to 10000 Å is preferable. In particular, in the case that a lighttransmitting electrode is used, 50 Å to 400 Å is preferable. Inaddition, in the case that a non-light transmitting electrode is used,1000 Å to 5000 Å is preferable.

[0081] Rhodium (Rh), iridium (Ir), silver (Ag), aluminum (Al) and thelike can be cited as a metal materials of a high reflectance which areused, specifically, in a reflecting electrode in a gallium nitride-based(at least gallium and nitrogen are included) semiconductor lightemitting device.

[0082] It is specifically preferable to use Rh as the material of theopen electrode. The electrode can be thermally stabilized and can have alow light absorption by using Rh. In addition, the contact resistancecan be lowered.

[0083] <3> Size and Form of Open Electrode

[0084] Though the relationships concerning the size of the openings ofthe electrode and the size of the recesses or protruding portions on thesurface of the substrate are not specifically limited, it is preferablefor at least two or more edges of recesses or protruding portions to becreated within one opening. Thereby, the light scattered or diffractedby the unevenness can be effectively emitted and at the same time, theuniformity of the light emission increases.

[0085] In addition, the open electrode is an electrode having aplurality of openings that penetrate to the surface of the p-typesemiconductor layer and that are surrounded by the electrode and it ispreferable for L/S≧0.024 μm/μm² to be fulfilled wherein the area of aportion surrounded by the outermost peripheral portion (total area ofthe electrode including the openings) is S and the total sum of thelength of the inner periphery of the openings is L. Thereby, asemiconductor light emitting device can be gained wherein light can beefficiently emitted from the surface of the p-type semiconductor layerto the outside and, in addition, Vf is low.

[0086] It is preferable for the respective openings of the plurality ofopenings to have approximately the same form and thereby, the creationof openings becomes easy and the distribution of emitted light withinthe surface becomes uniform. In addition, it is preferable for therespective openings to have approximately the same area and thereby, thedistribution of the emitted light within the surface becomes uniform.

[0087] In the case that openings are formed in a thick layer, the shape,the size and the like of these openings is controlled so that theefficiency of the light emission can be enhanced and the efficiency oflight generation can be increased. In particular, the more efficientemission of light becomes possible by controlling the length L of theinner periphery of the openings. When L/S becomes small, that is to say,when the total sum L of the length of the inner periphery of theopenings becomes small relative to the area S surrounded by theoutermost peripheral portion of the open electrode, the output to thep-type semiconductor layer side is lowered.

[0088]FIG. 13 shows the power conversion efficiency when the ratio ofthe openings remains the same, that is to say, when the total area ofthe openings remains the same while the length of the inner periphery ischanged. The area of the openings remains the same and thereby, thecontact area between the p-type semiconductor layer and the openelectrode remains the same so that Vf and the quantum efficiency areconsidered to be the same. It is understood from this figure that outputcan be enhanced by changing the length of the inner periphery of theopenings, even when the ratio of the openings remains the same. Then,according to the present invention, a semiconductor light emittingdevice of a high output can be gained by adjusting the length of theinner periphery of the openings in a range wherein L/S≧0.024 μm/μm² isfulfilled. Though the upper limit is not specifically set, in actualitywhen L/S becomes greater than 1 μm/μm², the size of one opening becomestoo small and the device becomes impractical.

[0089] The reason why the output efficiency from the p-typesemiconductor layer side is greatly affected by the length of the innerperiphery of the openings rather than by the area of the openings asdescribed above, is that an intense emission of light is observed at theboundary between the electrode and the p-type semiconductor layer andtherefore, an enlargement of the boundary, that is to say, a lengtheningof the inner periphery of the openings allows the efficient emission oflight. In order to further enlarge the boundary, the outermostperipheral portion of the p-side ohmic electrode is formed in a line ofa non-linear nature along the edge portion of the semiconductor layer,and thereby, the length of the boundary of the p-side ohmic electrodeand the p-type semiconductor can be enlarged so that the output can befurther increased.

[0090] A plurality of openings as described above can be created so thatthe respective openings have approximately the same shape and thereby,the plurality of openings can be efficiently created. Furthermore, thedistribution of the openings within the surface are easily made uniformso that stable light emission can be gained. As for the shape ofopenings, a variety of shapes, such as rectangular, circular, triangularand the like can be used. The shape is preferably a square and aplurality of openings is created so that the openings are uniformlydispersed with constant spaces vis-à-vis the neighboring openings andthereby, it becomes easy to gain a uniform light emission. In addition,the plurality of openings is created so that the areas of the openingsbecome approximately the same and thereby, a preferred opening shape canbe selected depending on the position wherein an opening is created.

[0091]FIGS. 14A to 14E show preferred shapes of the open electrode. InFIG. 14A, a p-side semiconductor layer 32 is formed on an n-sidesemiconductor layer 30 and an open electrode 34, which is a p-side ohmicelectrode, is formed on p-side semiconductor layer 32 and a p-side padelectrode 36 is formed as a portion of open electrode 34. In addition,an n-side pad electrode 38 is formed on n-side semiconductor layer 30that has been exposed through the etching of p-side semiconductor layer32. A plurality of circular openings is arranged in open electrode 34.FIG. 14B show open electrode with large size openings. FIG. 14C and FIG.14D only shows the opening electrode 34 and the pad electrode 36. Asshown in FIG. 14C, openings may be formed as slits, of which ends areopen. In this case, the ohmic electrode is like a combination of aplurality of line electrodes. The openings are preferably formed so thatcurrents are not concentrated locally. FIG. 14D shows a modified exampleof the shape of the openings, wherein a plurality of openings, in an arcform and arranged so as to be concentric, is provided with an n-side padelectrode (not shown) placed at the center. Such an opening shapeenhances the uniformity of the emitted light.

[0092] In addition, though the shape of the p-side ohmic electrode inthe cross section of the edge portion may be vertical, as shown in FIG.15A, it may, preferably, be a mesa(=trapezoid), as shown in FIG. 15B. Inthe case, particularly, of a gallium nitride-based compoundsemiconductor light emitting device, the device has a property whereinthe intensity of the emitted light is high at the peripheral portion ofthe p-side ohmic electrode and therefore, such a cross sectional edgeportion form, that is to say, a mesa allows light to be efficientlyemitted. In this case, it is preferable for the angle of taper θ of thecross sectional edge portion to be in the range of 30 degrees≦θ<90degrees. In the case that the angle of taper is 30 degrees or less, theresistance value of the p-side ohmic electrode becomes great in thetapered portion and therefore, it becomes difficult to effectivelyutilize the property that the peripheral portion of the electrode emitsintense light.

[0093] (2) Form of Semiconductor Light Emitting Device

[0094] According to the present invention, at least two semiconductorlayers and a light emitting region, of which the materials differ fromthat of the substrate, are formed on the surface of the substrate in alayered structure. That is to say, the substrate and the semiconductorlayers are made of different materials. Here, in the case that aninsulating substrate is used as the substrate, for example, in the casethat a gallium nitride-based (at least gallium and nitride are included)semiconductor layer is formed on a sapphire substrate, an electrodecannot be formed on the substrate and therefore, it is necessary to formtwo electrodes of an n electrode and p electrode on the same side of thedevice. At this time, for example, a nitride semiconductor deviceformed, in this order, of an n-type semiconductor layer, a lightemitting region, a p-type semiconductor layer is formed. By etching aportion of the p-type semiconductor layer until the surface of then-type semiconductor layer is exposed. A p-side electrode is formed onthe surface of the p-type semiconductor layer and an n-side electrode isformed on the exposed surface of the n-type semiconductor layer so thatthe respective electrodes are placed at the two vertexes diagonallyopposite to each other of the semiconductor device in a square form, asshown in the top surface view of the semiconductor layer of FIG. 16.

[0095] In this case, light emitted to the outside from the sides of thesemiconductor light emitting device is blocked by external connectionterminals, such as the n-side electrode and a wire connected to then-side electrode, formed on the sides by exposing the n-typesemiconductor layer.

[0096] As shown in FIG. 17, n-type semiconductor layer exposed islocated inside the p-type semiconductor layer so that the light emittingregion that emits light between the n-type semiconductor layer and thep-type semiconductor layer is provided on the entirety of outer sides ofthe semiconductor light emitting device to increase the efficiency oflight emission to the outside of the device. In the case of a devicewherein a p-type semiconductor layer, a light emitting region and ann-type semiconductor layer are layered, in this order, on a substrate,the exposed surface of the p-type semiconductor layer is provided insidethe n-type semiconductor layer so that the same effects can be gained.

[0097] In addition, as shown in FIG. 17, in the case a inner portion ofone-type semiconductor layer is taken away with etching so thatanother-type of semiconductor layer is exposed, a branch electrodeprotruding from a pad electrode for diffusing current is preferablyformed on the exposed semiconductor layer. This uniformalize the currentflow in the one-type semiconductor layer. In the case that the electrodewith openings is formed, the branch of the pad may be formed on theelectrode. More preferably, the branch is formed along the outerperiphery of the semiconductor. This further improves the uniformity ofthe light.

[0098] The external shape of the semiconductor light emitting device, asviewed from above, can be quadrangular, triangular or formed of otherpolygons. The exposed area of one-type semiconductor layer and theelectrode formed on the exposed layer is preferably formed so that aportion thereof extends toward the vertex of the light-emitting device.This makes current flow uniformly and such a configuration is preferablebecause light emission in the light emitting region becomes uniform.

[0099] In the case that a light emitting device of the present inventionis, for example, a gallium nitride-based (at least gallium and nitrideare included), mixture of fluorescent material including YAG and a resinare preferably formed on the surface of the light emitting device, inorder to gain a white light emitting device having a high efficiency. Alight emitting device having a variety of wavelengths of emitted lightand having a high efficiency of light emission is provided byappropriately selecting the fluorescent material.

[0100] The p-side electrode and the n-side electrode used in the presentinvention are the electrodes formed so as to contact with at least thesemiconductor layers and the materials thereof are appropriatelyselected to provide excellent ohmic properties for the contactedsemiconductor layers.

EXAMPLE 1

[0101] A sapphire substrate, of which a C plane (0001) is used as themain surface, having the orientation flat in an A plane (11-20), is usedas the substrate.

[0102] First, an SiO₂ film 30 that becomes an etching mask is formed ona sapphire substrate 10, as shown in FIG. 4A.

[0103] Next, a photomask of an equilateral triangle having a side of 5μm is utilized and the photomask is arranged so that one side of theequilateral triangle becomes perpendicular to the orientation flat whilethe respective sides of the equilateral triangle become approximatelyparallel to (1-100), (01-10) and (-1010), that is to say, an M plane andthen, after SiO₂ film 30 and sapphire substrate 10 are etched by 3 μm to4 82 m using RIE, as shown in FIGS. 4B and 4C, a repeating pattern ofprotruding portions 20 (hatched areas are unetched areas, that is tosay, protruding portions), as shown in FIG. 11B, is formed in thesurface portion of sapphire substrate 10 when SiO₂ film 30 is removed.As for the length a of one side of a recess, a=5 μm and as for aninterval b between a recess and a recess, b=2 μm. The pitch betweenprotruding portions (distance between the centers of neighboringprotruding portions) is 6.3 μm. In addition, the angle of inclination ofa side of a recess is 120 degrees.

[0104] Next, a buffer layer, which is made to grow at a low temperature,of AL_(x)Ga_(1−x)N (0≦x≦1), of 100 Å, is layered as an n-typesemiconductor layer on sapphire substrate 10 wherein the repeatingpattern of protruding portions 20 is formed and undoped GaN of 3 μm, Sidoped GaN of 4 μm and undoped GaN of 3000 Å are layered and then, sixwell layers and seven barrier layers, having respective film thicknessesof 60 Å and 250 Å, wherein well layers are undoped InGaN and barrierlayers are Si doped GaN, are alternately layered as an active layer of amulti quantum well that becomes the light emitting region. In this case,the barrier layer that is finally layered may be of undoped GaN. Here,the first layer formed on the buffer layer grown at a low temperature ismade of undoped GaN and thereby, protruding portions 20 are uniformlyfilled in so that the crystallinity of the semiconductor layer formed onthe first layer can have excellent properties.

[0105] After layering the active layer of a multi quantum well, Mg dopedAlGaN of 200 Å, undoped GaN of 1000 Å and Mg doped GaN of 200 Å arelayered as a p-type semiconductor layer. The undoped GaN layer formed asa p-type semiconductor layer shows p-type characteristics due todiffusion of Mg from the neighboring layers.

[0106] Next, starting from the Mg doped GaN, the p-type semiconductorlayer, the active layer and a portion of the n-type semiconductor layerare etched in order to form an n electrode so that the Si doped GaNlayer is exposed.

[0107] Next, a light transmitting p-side electrode made of Ni/Au isformed on the entirety of the surface of the p-type semiconductor layerand in addition, a p pad electrode made of Au is formed at a positionopposite to the exposed surface of the n-type semiconductor layer and ann electrode made of W/Al/W and an n pad electrode made of Pt/Au areformed on the exposed surface of the n-type semiconductor layer on thelight transmitting p electrode.

[0108] Finally, the wafer is cut into chips of quadrangular form andmounted on a lead frame with reflectors to gain a 350 μm□ semiconductorlight emitting devices. This chip is mounted on a lead frame with areflecting mirror to form a bullet-like LED.

[0109] The LED gained in such a manner have a light emission output tothe outside of 9.8 mW according to a lamp measurement for a forwarddirection current of 20 mA (wavelength=400nm).

Comparison Example 1

[0110] As a comparison example, a light emitting device is formed in thesame manner as in first embodiment without the provision of unevennesson the surface of the sapphire substrate and then, the light emissionoutput to the outside is 8.4 mW according to a lamp measurement for aforward direction current of 20 mA.

EXAMPLE 2

[0111] A sapphire substrate, of which a C plane (0001) is used as themain surface, having the orientation flat in an A plane (11-20) is usedas the substrate.

[0112] A process in the substrate and layering of an n-typesemiconductor layer to a p-type semiconductor layer are carried out inthe same manner as in first example.

[0113] Next, a p-type semiconductor layer made of Mg doped GaN, anactive layer and a portion of the n-type semiconductor layer are etchedin order to form an n electrode so that the n-type semiconductor layermade of Si doped GaN is exposed.

[0114] Next, a photomask having a pattern wherein equilateral triangleshaving a side of 5 μm, as shown in FIG. 16, are most densely filled perunit area is utilized so that a light transmitting p electrode made ofNi/Au is formed on almost the entirety of the surface of the p-typesemiconductor layer.

[0115] Furthermore, a p-side pad electrode made of Au is formed at aposition opposite to the exposed surface of the n-type semiconductorlayer on the light transmitting p electrode and an n electrode made ofTi/Al and an n pad electrode made of Pt/Au are formed on the exposedsurface of the n-type semiconductor layer.

[0116] Finally, the wafer is split into chips of quadrangular forms togain semiconductor light emitting devices. This chip is mounted on alead frame with a reflecting mirror to form a bullet-like LED.

[0117] The LED gained in such a manner has properties wherein thevicinity of the periphery of the p electrode emits light that is moreintense than that from other portions and therefore, the light emissionoutput is increased in comparison with first embodiment.

EXAMPLE 3

[0118] A sapphire substrate, of which a C plane (0001) is used as themain surface, having the orientation flat in an A plane (11-20) is usedas the substrate.

[0119] A process of the substrate and layering of an n-typesemiconductor layer to a p-type semiconductor layer are carried out inthe same manner as in first example.

[0120] Next, starting from Mg doped GaN, the p-type semiconductor layer,an active layer and a portion of the n-type semiconductor layer areetched in order to form an n electrode so that the Si doped GaN layer isexposed.

[0121] Next, a photomask of a square pattern is utilized so as to form ap electrode 104 made of Rh on almost the entirety of the surface of thep-type semiconductor layer. The shape of the openings is square, ofwhich side is 7.7 μm. The interval of the openings is 6.3 μm. Theaperture ratio of the opening is about 30%.

[0122] Furthermore, a p-side pad electrode made of Pt/Au is formed at aposition opposite to the exposed surface of the n-type semiconductorlayer on p electrode and an n electrode made of W/Al/W and an n padelectrode made of Pt/Au are formed on the exposed surface of the n-typesemiconductor layer.

[0123] Finally, the wafer is split into chips to gain semiconductorlight emitting devices. This chip is mounted on a lead frame with areflecting mirror to form a bullet-like LED.

[0124] The LED gained in such a manner has properties wherein thevicinity of the periphery of the p electrode emits light that is moreintense than that from other portions and in addition, a material havinga high reflectance of the wavelength of the emitted light is used forthe electrode so as to reduce the light component absorbed by theelectrode, and therefore, the light emission output is increased incomparison with first and second embodiments. The light emission outputis 13.2 mW according to a lamp measurement.

EXAMPLE 4

[0125] In the light emitting device of third example, p electrode isformed in a stripe form, as shown in FIGS. 14C. By adopting such astripe electrode structure, a current supplied from a p-side padelectrode to semiconductor layer is made uniform within the surface toincrease the efficiency of the light emission.

[0126] The stripes of the first electrode are created as openings thatexpose semiconductor layer and therefore, the length of the edge of theelectrode can be significantly increased and as a result, the efficiencyof the light emission is increased. At this time, it is preferable toachieve L/S≧0.024 μm/μm² wherein the value of S is gained by adding thetotal area Sa of openings 5 corresponding to the plurality of stripes,which exposes semiconductor layer, and area Sb of the electrode portionthat does not expose semiconductor layer, and the value of L is thetotal sum of the length of the circumferences of openings 5.

EXAMPLE 5

[0127] A sapphire substrate, of which a C plane (0001) is used as themain surface, having the orientation flat in an A plane (11-20) is usedas the substrate.

[0128] A process of the substrate and layering of an n-typesemiconductor layer to a p-type semiconductor layer are carried out inthe same manner as in first embodiment.

[0129] Next, the p-type semiconductor layer is etched until the Si dopedGaN layer is exposed from the inside of the p-type semiconductor layer,in particular, from the center portion of the p-type semiconductorlayer. The surface exposed as a result of etching at this time is formedso that portions thereof are extended toward the three vertexes formingthe shape of the semiconductor light emitting device, as shown in FIG.17.

[0130] Next, a photomask of a pattern wherein equilateral triangleshaving one side of 5 μm are most densely filled per unit area isutilized to form a p electrode 104 made of Rh in an equilateraltriangular form on almost the entirety of the surface of the p-typesemiconductor layer.

[0131] Furthermore, a p pad electrode, which is also a p diffusionelectrode, 106 is formed of Pt/Au on p electrode 104. This p padelectrode, which is also a p diffusion electrode 106, is provided byextending the pad electrode along the shape of the semiconductor lightemitting device that becomes an equilateral triangle, as shown in FIG.17. By providing this electrode, it becomes easy for a current touniformly flow through the entirety of the surface of the semiconductorlayer and therefore, this electrode functions as a diffusion electrode.

[0132] In addition, an n electrode made of W/Al/W and an n pad electrode103 made of Pt/Au are formed on the exposed surface of the n-typesemiconductor layer.

[0133] Finally, the wafer is split into chips of equilateral triangularforms to gain semiconductor light emitting devices. Such a lightemitting device is shown in FIG. 17, as viewed from above.

[0134] A light emitting device gained in such a manner has propertieswherein the vicinity of the periphery of the p electrode emits lightthat is more intense than that from other portions and in addition,wherein a material having a high reflectance of the wavelength of theemitted light is used for the electrode to reduce the light componentabsorbed by the electrode, and furthermore, wherein the light emittingregion of a multi quantum well structure is provided throughout theouter sides of the semiconductor light emitting device and therefore,the light emission output is increased in comparison with first to thirdembodiments.

EXAMPLE 6

[0135] A light transmitting resin containing Y₃Al₅O₁₂Y:Ce(YAG:Ce) havinga yttrium aluminum oxide-based fluorescent substance as a base offluorescent material is formed on the top surface and on the sides of asemiconductor light emitting device gained in fifth example.

[0136] A semiconductor light emitting device gained in such a manneremits white light having a high light emission output.

EXAMPLE 7

[0137] A sapphire substrate, of which a C plane (0001) is used as themain surface, having the orientation flat in an A plane (11-20), is usedas the substrate.

[0138] Next, following four types of protruding portions are made on thesurface of the substrate.

[0139] (i) An equilateral-triangle like protrusions as shown in FIG. 11Bare formed on the sappire substrate. Each triangle is arranged so thatone side thereof is perpendicular to the orientation flat surface of thesapphire substrate.

[0140] The triangles are arranged so that the vertex thereof headsinverse direction to the adjacent triangle. The length of a side of thetriangle is 5 μm and an interval between protruding portions is 2 μm.

[0141] (ii) A diamond like protrusions as shown in FIG. 11L is formed onthe surface of the substrate. The side lenght is 4 μm, and the intervalbetween protruding portions is 2 μm.

[0142] (iii) A hexagon like protrusion as shown in FIG. 11M is formed onthe surface of the substrate. The side lenght is 3 μm, and the intervalbetween protruding portions is 2 μm.

[0143] (iv) No protrusions are formed on the substrate surface.

[0144] Next, a buffer layer, which is made to grow at a low temperature,of AL_(x)Ga_(1−x)N (0≦x≦1), of 100 Å, is layered as an n-typesemiconductor layer on sapphire substrate 10 wherein the repeatingpattern of protruding portions 20 is formed and undoped GaN of 3 μm, Sidoped GaN of 4 μm and undoped GaN of 3000 Å are layered and then, sixwell layers and seven barrier layers, having respective film thicknessof 60 Å and 250 Å, wherein well layers are undoped InGaN and barrierlayers are Si doped GaN, are alternately layered as an active layer of amulti quantum well that becomes the light emitting region. In this case,the barrier layer that is finally layered may be of undoped GaN.

[0145] After layering the active layer of a multi quantum well, Mg dopedAlGaN of 200 Å, and Mg doped GaN of 200 Å are layered as a p-typesemiconductor layer.

[0146] Next, starting from the Mg doped GaN, the p-type semiconductorlayer, the active layer and a portion of the n-type semiconductor layerare etched in order to form an n electrode so that the Si doped GaNlayer is exposed.

[0147] Next, a light transmitting p electrode made of Ni/Au havingthickness of 60 Å/70 Å is formed on the entirety of the surface of thep-type semiconductor layer and in addition, a p pad electrode made ofPt/Au is formed at a position opposite to the exposed surface of then-type semiconductor layer and an n electrode made of W/Al/W and an npad electrode made of Pt/Au are formed on the exposed surface of then-type semiconductor layer on the light transmitting p electrode.

[0148] Light emitting power of bare chips in a wafer are measured with aprober. Results are shown in Table 1. In Table 1, the relative power isshown wherein the output-power of case (iv) is 1. TABLE 1 relative power(i) triangle 1.48 (ii) diamond 1.43 (iii) hexagon 1.48 (iv) flat 1 1

[0149] As shown in Table 1, more than 43% improvement is achieved withan uneven substrate. The light measurement without reflection mirrorsenhances the effect of the uneven substrate.

[0150] Finally, the wafer is cut into chips of quadrangular form andmounted on a lead frame with reflectors to gain a bullet-like LED. TheVf and power (wavelength 460 nm) at 20 mA of the devices are as follows:TABLE 2 V f (V) power (mW) Relative power (i) triangle 3.54 10.08 1.14(ii) diamond 3.55 10.01 1.13 (iii) hexagon 3.51 10.30 1.16 (iv) flat3.48 8.85 1

[0151] As shown in Table 2, more than 13% improvement is achieved withan uneven substrate. The best result is achieved with hexagon protrudingportions.

EXAMPLE 8

[0152] In this example, Rh electrode with openings is usedalternatively. Other constructions except p-electrode are the same asthose in Example 7. The shape of the openings is square, of which sideis 7.7 μm. The interval of the openings is 6.3 μm. The aperture ratio ofthe opening is about 30%.

[0153] The results with bare chips are shown in Table 3. In Table 3, therelative power is shown wherein the output-power of case (iv) is 1.TABLE 3 Relative power (i) triangle 1.54 (ii) diamond 1.56 (iii) hexagon1.65 (iv) flat 1

[0154] As shown in Table 3, more than 54% improvement is achieved withan uneven substrate.

[0155] The bullet-like LEDs, which emit 460 nm light, are formed toevaluate their Vf and output power at 20 mA. The results are shown inTable 4. TABLE 4 V f (V) power (mW) Relative power (i) triangle 3.8712.74 1.17 (ii) diamond 3.96 12.95 1.19 (iii) hexagon 4.08 13.06 1.20(iv) flat 3.97 10.85 1

[0156] As shown in Table 4, more than 17% improvement is achieved withan uneven substrate. Especially, the best results are obtained with thehexagonal protrusions.

[0157] As can be seen from Examples 7 and 8, a p-side electrode withopenings can cooperate with the unevenness of the substrate, and therebythe effect of the unevenness is considerably improved.

[0158] Although the invention has been described in its preferred formwith a certain degree of particularity, it is understood that thepresent disclosure of the preferred form has been changed in the detailsof construction and the combination and arrangement of parts may beresorted to without departing from the spirit and the scope of theinvention as hereinafter claimed.

What is claimed is:
 1. A semiconductor light emitting device comprisingtwo semiconductor layers and a light emitting region made of materialsdifferent from that of a substrate and formed in a layered structure ontop of the surface of the substrate so that light generated in the lightemitting region is emitted from said upper side semiconductor layer orlower side substrate, wherein at least one recess and/or protrudingportion for scattering or diffracting light generated in said lightemitting region is created in the surface portion of said substrate andsaid at least one recess and/or protruding portion is in a form thatprevents crystal defects from occurring in said semiconductor layers. 2.The semiconductor light emitting device according to claim 1, whereinsaid recess and/or protruding portion is in a form having, as acomponent side, a line that crosses a plane approximately parallel tothe stably growing face of said semiconductor layers.
 3. Thesemiconductor light emitting device according to claim 1, wherein saidrecess and/or protruding portion is a polygon having a vertex in a planeapproximately parallel to the stably growing face of said semiconductorlayers and having, as component sides, lines that cross planesapproximately parallel to the stably growing face of said semiconductorlayers.
 4. The semiconductor light emitting device according to claim 1,characterized in that, assuming a polygon that has component sides inthe stably growing face of said semiconductor layers, said recess and/orprotruding portion is in a shape of another polygon having, as componentsides, lines that are perpendicular to line segments connecting thecenter and vertex of the first polygon.
 5. The semiconductor lightemitting device according to claim 1, wherein said recess and/orprotruding portion forms a pattern where its form is repeated.
 6. Thesemiconductor light emitting device according to claim 1, wherein saidsemiconductor layers are made of III-V group elements-basedsemiconductors.
 7. The semiconductor light emitting device according toclaim 1, wherein said semiconductor layers are made of GaN-basedsemiconductors.
 8. The semiconductor light emitting device according toclaim 2, wherein said surface of the stable growing substrate of thesemiconductor layers is an M plane {1-100} of a hexagonal crystal. 9.The semiconductor light emitting device according to claim 1, whereinsaid substrate is selected from the group consisting of a sapphiresubstrate, an SiC substrate and a spinel substrate.
 10. Thesemiconductor light emitting device according to claim 1, wherein saidsubstrate is a C plane (0001) sapphire substrate.
 11. The semiconductorlight emitting device according to claim 10, wherein the stably growingface in said semiconductor layers is a surface parallel to the A plane{11-20} of said substrate.
 12. The semiconductor light emitting deviceaccording to claim 3, wherein the polygon of said recess and/orprotruding portion is selected from the group consisting of a triangle,a parallelogram and a hexagon.
 13. The semiconductor light emittingdevice according to claim 3, wherein the polygon of said recess and/orprotruding portion is selected from the group consisting of anequilateral triangle, a rhomboid and a regular hexagon.
 14. Thesemiconductor light emitting device according to claim 1, wherein thedepth of said recess or the height of said protruding portion is notless than 50 Å and not more than the thickness of the semiconductorlayers grown on said substrate.
 15. The semiconductor light emittingdevice according to claim 2, wherein the lenght of the component side ofsaid recess and/or protruding portion is not less than λ/4, where thewavelength of emitted light in said semiconductor is λ.
 16. Thesemiconductor light emitting device according to claim 2, wherein thelength of the component side of said recess and/or protruding portion isnot less than λ/4n, where the wavelength of emitted light in saidsemiconductor is λ and the index of refraction of said semiconductor isn.
 17. The semiconductor light emitting device according to claim 2,wherein the length of the component side of said recess and/orprotruding portion is not more than 100 μm.
 18. The semiconductor lightemitting device according to claim 2, wherein the length of thecomponent side of said recess and/or protruding portion is not more than20 μm.
 19. The semiconductor light emitting device according to claims1, wherein the surface of said semiconductor layers is of a concaveand/or convex form.
 20. A semiconductor light emitting device comprisinga substrate, a plurality of semiconductor layers formed on saidsubstrate and made of different materials from that of said substrateand an ohmic electrode formed on the surface of the top layer of saidsemiconductor layers so that light generated in said semiconductorlayers is emitted from said ohmic electrode or from said substrate,wherein at least one recess and/or protruding portion for scattering ordiffracting light generated in said semiconductor layers is created inthe surface of said substrate and the cross section of said recess is ina form of a reversed trapezoid and the cross section of said protrudingportion is in a form of a trapezoid.
 21. The semiconductor lightemitting device according to claim 20, wherein said ohmic electrodecovers almost the entirety of the surface of the top layer of saidsemiconductor layers.
 22. The semiconductor light emitting deviceaccording to claim 20, wherein the taper angle of the side of saidrecess or protruding portion is not less than 90 degrees and not morethan 160 degrees.
 23. A semiconductor light emitting device comprising asubstrate, a plurality of semiconductor layers made of materialsdifferent from that of said substrate and an ohmic electrode coveringalmost the entirety of the surface of the top layer of saidsemiconductor layers so that light generated in said semiconductorlayers is emitted from said ohmic electrode, wherein at least one recessand/or protruding portion for scattering or diffracting light generatedin said semiconductor layer is created in the surface of said substrateand at least one opening is created in said ohmic electrode.
 24. Thesemiconductor light emitting device according to claim 23, wherein eachof said openings has inside at least one step portion of said recessesor protruding portions.
 25. The semiconductor light emitting deviceaccording to claim 23, wherein the relation ship of L/S≧0.024 μm/μm² issatisfied where L is the total length of the outer periphery of saidopening or slit and S is the area of said ohmic electrode including theinside of said opening or slit.
 26. The semiconductor light emittingdevice according to claim 23, wherein said ohmic electrode is an alloyor a multilayer film including at least one type selected from the groupconsisting of Ni, Pd, Co, Fe, Ti, Cu, Rh, Au, Ru, W, Zr, Mo, Ta, Pt, Ag,and oxides or nitrides of them.
 27. The semiconductor light emittingdevice according to claim 23, wherein said ohmic electrode is an alloyor a multilayer film including one type selected from the groupconsisting of rhodium (Rh), iridium (Ir), silver (Ag) and aluminum (Al).